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Franklin
06-25-2005, 12:15 PM
http://www.hydrofoil.com/whyhydrofoil.htm (http://www.hydrofoil.com/whyhydrofoil.htm)

http://www.hydrofoil.com/reference.htm (http://www.hydrofoil.com/reference.htm)

http://www.hydrofoil.com/gallery.htm (http://www.hydrofoil.com/gallery.htm)

Chili 18
06-26-2005, 09:48 PM
Cool Stuff

Formula Jr
07-19-2005, 03:33 PM
You would have to redefine what a "boat" is in order to come up with some way to frame this question correctly.
First, lets define a Mach Number:
A number representing the ratio of the speed of an object to the speed of sound in the same medium.
In air; a Mach number can vary slightly due to changing air density.
At Sea level Mach 1 is about 762 MPH.
At 30,000 feet it is about 678 MPH.

The speed of sound in Water is about 3315 MPH.
Sound waves, "compression waves" propagate much faster
in denser materials.

There is also supercavitation to consider.

http://www.subsim.com/ssr/page33.html

But this would be a sub and not a traditional boat.

If we define a mach one boat as beaking the air Sound Barrier, 762 MPH, then you have to wonder what still defines it as a boat and what now defines it as a surface effect flying vehicle that can also float at rest.
Any control fin or object of the "boat" would no longer really be in contact with water at speed, but in an envelope of water vapor. I think you can make such a vehicle go Mach I, but the physics involved always puts that vehicle outside of the definition of a boat.

Franklin
07-20-2005, 10:26 AM
"You would have to redefine what a "boat" is in order to come up with some way to frame this question correctly.
First, lets define a Mach Number:
A number representing the ratio of the speed of an object to the speed of sound in the same medium.
In air; a Mach number can vary slightly due to changing air density.
At Sea level Mach 1 is about 762 MPH.
At 30,000 feet it is about 678 MPH.
The speed of sound in Water is about 3315 MPH.
Sound waves, "compression waves" propagate much faster
in denser materials.
There is also supercavitation to consider.
http://www.subsim.com/ssr/page33.html
But this would be a sub and not a traditional boat.
If we define a mach one boat as beaking the air Sound Barrier, 762 MPH, then you have to wonder what still defines it as a boat and what now defines it as a surface effect flying vehicle that can also float at rest.
Any control fin or object of the "boat" would no longer really be in contact with water at speed, but in an envelope of water vapor. I think you can make such a vehicle go Mach I, but the physics involved always puts that vehicle outside of the definition of a boat."

No, nobody has to do irrelevant and specious crap like "You would have to redefine what a "boat" is in order to come up with some way to frame this question correctly." Anyone with common sense knows a boat is a vehicle that must operate on the surface of the water because it's not an airplane, submarine or torpedo.

Franklin
07-20-2005, 11:27 AM
An alternative to hydrofoil based configurations could be a hybrid approach with a surface hull incorporating submerged appendages based on supercavitating concepts.

http://www.ctechdefense.com/speed.html

2509 West 19th Street, Port Angeles, WA 98363
PHONE (360) 452-2275 * FAX (360) 452-2297 * info@ctech.esdcorp.com

Underwater Speed Limits
(Following is the full text submitted to Scientific American. The published version was shortened for editorial reasons.)

"There appear to be two conceptual ways of approaching supercavitation. The generally accepted one derives from propeller cavitation theory and holds that the water is essentially boiled by dropping its pressure via abrupt acceleration. This creates a source of gaseous water vapor which creates the cavitation bubble. It is generally assumed that the cavitation bubble is filled with this water vapor. Indeed, in low speed (say torpedoes) supercavitation applications the cavity size is usually enhanced with ventilation gases. This fits well with the understanding that gas creates the bubble in the first place and appears to work well within that context. It also fits comfortably in the general framework of marine engineering.

Last September, at an ONR sponsored Supercavitation Conference, Dr. Kirschner (of Anteon Corporation) and I were discussing the idea of a theoretical speed limit for supercavitating objects, assuming material strength issues could be overcome. As previously mentioned, conventional wisdom holds that the cavity is created by the water vapor and therefore, at some speed, the volumetric rate at which vapor can be generated will become insufficient to support the formation of a cavitation bubble which will clear the body. In other words, at some velocity the rate at which the water boils will become insufficient to fill the volume of the "hole" in the water created by the passage of the projectile and the cavity will collapse.

For whatever reason, I have a different mental picture of how the bubble is created, perhaps due to my background in hypersonics in graduate school. In that field discontinuities and rarified flows are encountered in the course of normal business. I do not know if anyone else shares this view but Dr. Kirschner and I have discussed it at some length. In any case, I believe the process is fundamentally one of momentum transfer. The cavitator, be it a disk or cone or whatever, imparts a significant radial velocity (relative to the axis of flight) to the water it comes in contact with. In effect the water is thrown violently to the side. It therefore has a high radial momentum that is resisted by the pressure of the water around it. This pressure serves to slow its radial velocity and will bring it to a stop over a finite time. The accepted definition of cavitation number is compatible with this idea. In the meantime, assuming a circularly symmetric cavitator, a round "hole" has been created in the water. What is in this hole, other than the projectile? I believe it is a vacuum, at least initially. Of course the water on the interior face of the bubble begins to boil, but it can only boil so fast, even in a hard vacuum. At slow velocities the rate of boiling can create a fairly decent partial pressure of water vapor in the cavity. In the limit case, as velocity increases, the pressure inside the cavity in the vicinity of the projectile will go to zero. Eventually the pressure acting on the water will reverse its radial velocity and cause the cavity to close. However, the projectile will be long gone by that point. If this approach is correct then, except for finding a material to withstand the steady state stagnation pressure, there may be no hydrodynamic upper limit to the velocity of a supercavitating body.

In any case, perhaps there is room for both viewpoints. In fact, they may very well be opposite sides of the same theoretical coin. I would certainly be interested to know what other people in the field thought of this approach. Perhaps it would provide an interesting topic of discussion within the article?"

Formula Jr
07-21-2005, 05:20 AM
No. This would be "specious and irrelevant." :hyper:

http://www.epud.net/%7Eowen/mach1.jpg

RedDog
07-21-2005, 09:12 AM
No. This would be "specious and irrelevant." :hyper:

http://www.epud.net/%7Eowen/mach1.jpg

now that is funny.....